The proliferation of imaging technology combined with ever increasing computational processing power has lead to many advances in the area of document analysis systems. A significant proportion of office documents are generated using structured text/graphics editing applications, such as Microsoft™ Word™ and Microsoft™ Powerpoint™. In addition to formatted text editing, these text/graphics editing applications include basic figure drawing tools and options. An important class of document analysis applications, referred to as “scan-to-editable” applications, process a bitmap representation of a document to generate an electronic version of the document that can be viewed and edited using such editing applications.
Figure drawing options in a typical structured text/graphics editing application include freeform line drawing, template shapes and connectors (i.e., dynamic line objects that connect to and/or between template shapes within a document). The text/graphics editing applications may also include colouring, filling, layering and grouping options for sets of graphical objects. Many commonly used geometric shapes can be created using template shapes. A user may prefer to use a template shape rather than drawing the shape using freeform lines, since this option can be faster, more accurate in terms of representation of the desired shape, and easier to edit at a later time. The Microsoft™ AutoShapes set includes a number of examples of template shapes which can be manipulated within editing environments such as Microsoft™ Word™ and PowerPoint™. Other template shapes may be found in OpenOffice.org™ editing applications, such as the Writer™ and Impress™ applications.
Techniques exist for detecting overlapping shapes in the case where these either have a solid fill or are line shapes with no fill. However, these techniques do not handle the case where the upper layer shape has a partial transparency, such that the lower layer shape is partly visible underneath.
Other techniques exist that represent a single object as a transparent graphical object for the purpose of photo-compositing. However, these techniques do not handle the intersection of a transparent object with a second object and can only find objects with a restricted set of colours on the outer boundary of the colour space representation.
Techniques also exist for detecting transparent regions from video based on processing multiple video frames. However, these techniques do not handle the intersection of transparent regions and require at least two images, the difference between the two images being attributed to the presence of a transparent object in one image.
A need exists for techniques of detecting and reconstructing partially transparent overlapping graphical objects from a single image.